1. Field of the Invention
The present invention relates to a tuning method of an external cavity laser diode (“ECLD”), a variable wavelength laser module, and a program of an ECLD tuning, and particularly to a tuning method of an ECLD and a program by which the optical power is increased and the single mode characteristic is improved, and a variable wavelength laser module using an external cavity semiconductor laser comprising an external resonator.
2. Description of the Related Art
A current optical storage disk typified by a CD, a DVD, a Blu-Ray disk, or another similar optical storage disk has a capacity of approximately 50 GB at maximum.
However, to deal with the digital broadcasting that will fully replace the current system in 2011, it is an urgent requirement to develop a recording medium having a large amount of capacity and a high transfer rate for video archive purposes.
A holographic memory has received attention as a next-generation optical storage that meets the requirements described above. A medium used in a holographic memory is typically known for its behavior in which a change in temperature changes the refractive index of the medium or expands or shrinks the medium so as to change the spacings between recording interference fringes.
Therefore, a light source used with a holographic memory or any other similar recording medium is required to change the wavelength of the light emitted therefrom in order to deal with the changes described above.
To this end, a variable-wavelength external cavity laser light source has been proposed in which a laser and a grating are combined and the angle of incidence of the laser beam with respect to the grating is changed in a θy direction to change the wavelength of the laser beam (for example, see Japanese Laid-open Patent Application No. H06-69582 or U.S. Pat. No. 5,387,998A).
In such a variable-wavelength external cavity laser light source, a method for tilting the grating to substantially maximize the feedback power has also been proposed (for example, see Japanese Laid-open Patent Application No. 2003-23197 or U.S. Pat. No. 6,807,217 B2).
In the variable-wavelength external cavity laser light source described above, it is necessary to precisely mount the grating with respect to the laser beam and precisely control the wavelength.
However, there is a concern that changes in temperature, aged deterioration, and other factors cause the optical axis of the laser beam to shift not only in the θy direction (as explained below) but also in other directions. The shift of the optical axis of the laser shift not only reduces the optical power but also degrades the single-mode characteristic or the contrast ratio (as explained below) and other characteristics, resulting in degradation in the characteristics required in the laser source or a storage system including the same.